Example: Mössbauer spectroscopy: Ferrocene

Download Mossbauer.run

By default in ADF the electron density at the nuclei is calculated, no input key is required. The electron density at the nuclei could be used for the interpretation of isomer shifts in Mössbauer spectroscopy. The absolute electron density at a nucleus heavily depends on the accuracy of the basis set in the core region of this nucleus, especially if relativistic effects are included. Important is to use the same basis set, same exchange correlation functional, same numerical accuracy, if electron densities at nuclei in different molecules are compared. For the calculation of Mössbauer quadrupole splittings the key QTENS is required. For 57 Fe quadrupole splittings will be written in units of mm/s, used in Mössbauer spectroscopy Example shows a calculation on ferrocene with a non-relativistic, and two with a scalar relativistic ZORA Hamiltonian using a different all electron basis set.

First a non-relativistic calculation.

$ADFBIN/adf << eor
title ferrocene

Atoms
    FE        0.000000    0.000000    0.000000
    C         1.215650    0.000000    1.600813
    C         0.375656   -1.156152    1.600813
    C        -0.983481   -0.714541    1.600813
    C        -0.983481    0.714541    1.600813
    C         0.375656    1.156152    1.600813
    C         1.215650    0.000000   -1.600813
    C         0.375656    1.156152   -1.600813
    C        -0.983481    0.714541   -1.600813
    C        -0.983481   -0.714541   -1.600813
    C         0.375656   -1.156152   -1.600813
    H         2.310827    0.000000    1.629796
    H         0.714085   -2.197727    1.629796
    H        -1.869498   -1.358270    1.629796
    H        -1.869498    1.358270    1.629796
    H         0.714085    2.197727    1.629796
    H         2.310827    0.000000   -1.629796
    H         0.714085    2.197727   -1.629796
    H        -1.869498    1.358270   -1.629796
    H        -1.869498   -1.358270   -1.629796
    H         0.714085   -2.197727   -1.629796
End

xc
 gga blyp
end

Basis
     Type TZP
     Core none
End

qtens

NumericalQuality Good
exactdensity

End Input
eor

Next the scalar relativistic ZORA calculations. ADF will also calculate the quadrupole splittings including the small component density, also called SR ZORA-4. The only difference is the RELATIVISTIC keyword:

relativistic scalar zora

Next a scalar relativistic calculation is performed with a much larger basis set (QZ4P) in the core region. Changing the basis set will have a large effect on the electron density at the nucleus and a noticeable effect on the calculated quadrupole splittings.

Basis
     Type QZ4P
     Core none
End
relativistic scalar zora